Provider backbone bridging or provider backbone bridges (PBB) is an Ethernet-based technology that enables the layering of a network into customer and provider domains with complete isolation between customer and provider MAC addresses. This technology is currently being formalized as an IEEE standard identified as IEEE 802.1ah. Provider backbone bridging is implemented between provider edge (PE) devices by adding a provider backbone header that includes a backbone source address (B-SA), a backbone destination address (B-DA), a backbone VLAN ID (B-VID), and a service instance VLAN ID (I-VID). Within a provider backbone bridging domain, packets are forwarded based on media access control (MAC) learning, loop avoidance is accomplished through Spanning Tree Protocol (STP), and B-VIDs are used for broadcast containment.
At the edges of a provider backbone bridging domain (e.g., at the PBB PE devices), forwarding information bases (FIBs) are populated with customer source MAC address (CMAC) and backbone source MAC address (BMAC) associations which are obtained through MAC address learning. In particular, a customer packet with a customer source address that enters the provider backbone bridging domain at a first PBB PE device is mapped to a backbone source MAC address, which is the source MAC address of the PBB PE device at which the packet entered the provider backbone bridging domain.
In order to provide failure protection between customer and provider domains, a customer edge (CE) device may be linked to two different PBB PE devices, a practice referred to as “dual-homing.” When a CE device is dual-homed, other PBB PE devices in the PBB domain will learn CMAC-to-BMAC associations for whichever link is being used to send traffic between the CE device and the two PBB PE devices to which the CE device is connected. As long as the link between the PBB PE device and the CE device is active, the learned CMAC-to-BMAC associations at the other PBB PE devices are valid and customer traffic will be successfully switched across the PBB domain to the target CE device.
However, if the link between the active PBB PE device and the target CE device fails or the active PBB PE itself fails, CMAC-to-BMAC associations learned at the other PBB PE devices will cause traffic to be sent to the target CE device via the failed link and/or the failed PBB PE device. Traffic that is sent to the target CE device via the failed link or the failed PBB PE device will not make it to the CE device and will eventually be lost without the knowledge of the sending PBB PE device at the other end of the PBB domain. This loss of traffic, often referred to as “black-holing,” will continue until the CMAC-to-BMAC associations are aged out of the FIBs at the respective PBB PE devices or until a new packet is sent from the CE device with the same CMAC such that a new CMAC-to-BMAC association can be learned through the native Ethernet learning process. Relying on aging or the transmission of a new packet to trigger a new CMAC-to-BMAC association may result in noticeable disruptions to the customer, especially with regard to time-sensitive applications such as real-time voice and streaming video.